Recently, the housings of portable terminal devices typified by cellular phones, smart phones, Personal Digital Assistants (PDAs), and tablet type terminals have been required to reduce the dimensions and weight from the viewpoint of compactness and lightweightness. Accordingly, demands have arisen for more compact antenna devices. It has also been required to allow a single portable terminal device to communicate with a plurality of radio systems using different frequency bands.
Conventionally, therefore, a multifrequency antenna device has been proposed, which has, for example, the second antenna element formed from a monopole element and provided in a direction opposite to the first antenna element formed from a folded element with a stub at a position near the feeding point of the first antenna element.
In these conventionally provided multifrequency antenna devices, although it is possible to independently adjust the first resonance caused by the folded element and the second resonance caused by the monopole element, there occurs a band in which radiation efficiency deteriorates due to parallel resonance between the first resonance and the second resonance, resulting in difficulty in achieving wider bandwidth.